An aromatic dialdehyde, particularly terephthalaldehyde, is a bifunctional compound which has been noted as a new basic material having various uses. For example, it is used as a basic material for liquid crystals; conductive polymers; or high temperature engineering polymers such as polyimine, polystyrylazine or polybenzimidazole, etc., and also is applied to fluorescent brightening agents or specialty polymers. Further, it is applied as a basic material for specialty monomers such as cyclohexanedimethanol, p-hydroxybenzoic acid, hydroquinone, p-hydroxymethylbenzoic acid, etc.
Terephthalaldehyde is typically synthesized by a liquid phase reaction from di- or tetrachlorinated side chain derivatives of p-xylene. However, it is not easy to produce it in large scale, and so has some limitations to be developed for various uses. However, a method for preparing terephthalaldehyde by one step gas phase oxidation reaction from p-xylene was developed and commercialized, thereby receiving more interests for its production and use in a large scale.
U.S. Pat. No. 3,597,485 describes a method for preparing terephthalaldehyde through one step gas phase oxidation reaction of p-xylene by using a catalyst consisting of tungsten and molybdenum.
U.S. Pat. No. 4,017,547 describes a catalyst consisting of tungsten, molybdenum, and bismuth.
U.S. Pat. No. 5,324,702 describes a catalyst wherein iron, zinc, vanadium, molybdenum, tungsten, etc. are incorporated to deboronated borosilicate crystal molecular sieve via chemical vapor deposition.
Also, U.S. Pat. No. 6,458,737 B1 discloses a multi-component oxide catalyst comprising tungsten and antimony.
However, the above prior arts merely disclose catalysts used for preparing terephthalaldehyde by one step gas phase oxidation reaction, or the preparation method per se, and provide no information on the separation or purification method for obtaining highly pure terephthalaldehyde. When the above prior catalysts are used, the desired terephthalaldehyde is obtained in a low yield, or in a low selectivity with a high yield, and so its separation and purification are not easy. Further, due to the use of multi-component oxide complex, it is not easy to prepare a catalyst having homogenous composition and property. Furthermore, since the catalysts of the prior arts include some components having low thermal stability, their life is short, and so they have some limitations for industrial application.